Open-Source DC solar system development, i want your opinions please!

ArjenCNX

Dear Forum members, I'm Arjen, and i am with a small group of engineers that call them selves Build for life. Currently we are working on a small DC solar system that has some unique attributes, let me explain: 

Currently smaller home systems seem hard to find, the choice is usually to get separate batteries, charge controllers and inverters, and the users are expected to either do  DIY job, or get an installer to get everything running.  These products are usually not really made to work together, as in they cannot communicate with each other and the status of the system as a whole is thus not always easy to assess.  Next to this there seems to be no open-source solutions available in the market for a rather important thing for many people, when the units run out of warranty/support, you often just have to buy a new one. 

I can see many have now adopted to using those battery/inverter combo devices such as ecoflow and bluetti, but this doesnt really solve the problem for permanent installs, is still not open-source and assumes you run everything from 120/230VAC. 

Thus my conclusion has been the as follows (and i would love some comments on this) 

• There are no serious open-source solutions
• most solutions out there require the user to scavenge for parts that are DIY'd together, requiring knowledge many will not have
• Most solutions will rely 100% on AC 120~230V appliances for everything, and this is not a very efficient way of using energy as in many cases things will go from DC>AC>DC>load.  since inverters are about 85% efficient this wastes up to 35% power
• There does not seem to be any brand that offers a family of products that solves all the basic needs of every household 

Thus we have been thinking about a system that does just that, there were a few basic technical requirements that we came up with, devices should be able to communicate, so we can control everything centrally allowing for easy energy consumption control and planning (home-automation) and optimal safety. Quality standard should be very high, as you depend on your solar system for most energy needs. Modularity is important so that redundancy can be had, with spare modules if needed, plus the fact that this type of Lego-style system can be configured to any specific needs plus that this makes the entry cost in to the system lower.

Thus we have come up with the following modules, they are connected to a rail, and have connectors on the side so they can be plugged together to share power and data connections. (no more cables and DIY work)

1. Battery Module 480Wh  up to 4 in one system 
2. Controller module, with touchscreen and advanced home automation interface, WiFi etc. + all the power outputs of the power output module
3. MPPT charger 600W 36~80V 
4. Inverter 500W  
5. Power output module with USB-C 100W / 2X USB-A 15W + 5 outputs for LED's and fans 
6. Computer module (full PC function, using Intel N100 SBC 
7. 4G modem module with external antenna  / Amplifier HIFI module. 
   
8. Lighting: top class quality LED lighting, CRI>97, flicker free 2700~5000K adjustable 3 sizes, 500/1000/1500 lumens 
9. IR remote light power switches
10. ceiling fans in 2 sizes

Lighting and fans and USB power plugs are connected via POE style network cables for power and data, up to 48W over one line, ability to daisy chain things like lights and fans. CAT6a cable is cheap and easy to get and make to length where ever needed. it also enables communication, so we can remotely control and time anything that is connected this way. 

this system is designed for tiny homes, off-grid buggout locations, cabins, vans, boats, and anyone off-grid that wants a dependable and expandable system that is open-source, thus serviceable and where community can get involved with new module designs, new functions, new firmware and so on.   

Things i have no solution for as of yet:  

Fridges, (yes it can run off the inverter, but i would prefer an independent solution)
Water pumping, especially deep well pumping
Air-conditioning 
things you will tell me about. 

Thanks for chiming in, i hope i learn something here, your comments will change the development of this system

JRHill

Interesting project. So up to 4 battery modules planned. Can additional charge controllers and inverters be added as well?

How about the temperature limitations of lithium chemistries? Some folk only want lead batteries because of limitations of lithium so will this system allow for configuration to use lead batteries including their charging requirements?

Communication: Unattended operation and remote access including monitoring AND remote adjustment of parameters? Security? Hosted/cloud based or XYZ? Subscription?

I think an important part would be generator support for those times when the sun isn't shining. Not just for higher, planned loads but also to recharge the battery bank. Also for automatic generator start, warm-up, run-time, cool down and shut down.

Dave Angelini

"Currently smaller home systems seem hard to find, the choice is usually to get separate batteries, charge controllers and inverters, and the users are expected to either do  DIY job, or get an installer to get everything running."  

I think you are wrong here about hard to find!  There are many places for this. There are even all in one solutions that are fairly simple now.  Even Costco sells them.  The store here has it all ! Go on their website!
https://www.solar-electric.com/

ArjenCNX

JRhill,  thanks for your comment, Generally charging is done with a generator that supplies AC 120 or 230V, so what that would take is a module that contains a AC>DC converter with current limiting that can ideally trigger the generator at a set battery level, or charge the back-up from the grid. OK, ill check that out and see how we would go about that, but it sounds like a general purpose switch-mode power supply with constant current mode, wide input, and perhaps about 500W of charge capacity ( batteries take up to 10A of charge current at up to 26V per pack)   then it can also be the grid-side charge interface, that would be useful for those that just want a fancy UPS system as well. ill add this to the list of modules to be developed, it just makes sense.   Thanks sir! 

ArjenCNX

Hi Dave, thanks for your comment,   I know systems exists that are made for off-grid, and im not doubting high-quality systems can be had as well, for myself this would be adequate as im an engineer, installation would not pose any difficulty for me. However, there seems to be no open-source solutions out there and personally i would prefer a system that is so nice that it need not be hidden in some cabinet, i was thinking of: open-source, modular, repairable, efficient, kind of like B&O meets open-source solar. I'm also not aiming to build something very low cost, it would be significantly cheaper then a full inverter output set with kilo-watts worth of storage and output power but since the aim is to "build for life" quality will take the center stage in this design. Since it will be open-source others are free to take blocks of the design and create a lower cost solution, in fact, i'd be glad if someone did do that as well.  

ease of installation though is something i care about, i want a system that my wife can install without my presence and i think this is possible to do.  ill post some images today of what i have so far, and i hope people here would be so kind as to share their thoughts. 

Thanks again

Arjen & Build for life team

littleharbor2

EG4 is making some very nice equipment these days large capacity wall/floor mount batteries, high output inverters, all integrated

Dave Angelini

And probably the best out there now is Midnite A10. I have been using them alot since Schneider announced the demise of the XW platform.

And then there is Apollo. H voltage PV input and expandable battery.

The real concern now is if China will play nice as so much of this industry depends on Communist's.

Dave Angelini

The store here sells Midnite and you should consider using NAZ as this forum may go away if people do not patronize the companies that sponsor the content! Tell that to NAZ if you use them please!

ArjenCNX

interesting stuff, and yes the China tariff situation is indeed really stirring up some... dust.  I think its a good case for open-source though, as it can be made anywhere by anyone. but not at any price, it's complicated for sure. what i am seeing still is a gap in the market for people that cant afford to go all out on storage and power delivery, but still want a nice system that is highly efficient. once you go AC, this becomes very hard to control, as you'd be using general purpose devices, that cannot communicate with the power delivery system. Running an inverter even at idle takes tens of watts, enough to run lights or a computer just in losses, this also kind of puts me off. only way out is to see how much functions can be run from DC, but there you must make your own appliances, or at the least set a quality and efficiency standard that makes it worth while. Open-source can help there as well to level the playing field and to make quality insightful instead of having it all black-box. even if the service is good from a supplier, if i can fix it myself i'd prefer it, its faster, cheaper and self-reliant. 

Dave Angelini

Not sure what country you are in but in most developed parts of the world DC wiring and DC loads in
residential/Commercial are not up to building code. They are not insurable unless you buy a specific policy from Lloyds of London. Even then it would still not meet the building code.

What you are describing is from the very early days of Solar and this forum has some of what you call open source still in here from 15+ years ago. To me open source is what we use to get into modbus, canbus and others for communicating with a battery from an Inverter for closed loop charging.

As for fixing it yourself, there still is some board level swapping going on but even that is rare. We do repairs of devices with spare devices. For a long time now ! At HP this was in the late 1980's for instrumentation repair.

Good Luck!

ArjenCNX

wow, you worked at HP in their heydays, that is really cool, nothing nicer then some good 80's-90's HP gear, im collecting some of those, and they get good use in the lab! i think you cannot find a better example for built for life then old HP gear, though some are very hard to repair (Boy have i spent some time on fixing my old impedance analyzer and spectrum analyzers!! )   

So when i say open-source, i mean 100% open, including PCB design files in Kicad, Firmware source code, mechanical design files and so on. i have not found any good projects that are complete and of high quality that offer this. 

About DC lines in the house, i will have to check what regulations you are referring to, im not familiar with that, but what we propose in the design is very similar to POE, and this is widely adapted. 

Also this smaller system is a runner up to a 220V system with high power capacity, i thought it prudent to start with a smaller system to fill a niche in the market that is currently under-served in my opinion especially for the less technically astute people. adding new functions or more capacity in my design does not even require a screwdriver, just slide on a new module and you are done. 

It's intended for cabins, RV's, tiny homes and so on, places where high power 220V is not really needed. (think of an island hotel with 20 small cabins) 

We are still working on the design now, the second solar MPPT charger board design is now done, and with GaN fets should get near 97% efficiency, at 600W. Boards are on the way for testing now, ill show results once i have them. 

Dave Angelini

Here is a link to HP in the good old days.

https://www.hewlettpackardhistory.com/collection/instrumental-ideas/

I think there is a pix in one of those of Dave Packard wearing his train engineer garb at a hardware store in Palo Alto in the 1980's. Below is the 5360 frequency counter built at HP Santa Clara division. I worked there but after this counter was used to correct the speed of light measurement.

The HP 5360A: Measuring to the Moon

Enlarge 

Share this piece of history

Date: 1969

The HP 5360A computer counter could tabulate and process reflected signals with an accuracy several orders of magnitude beyond its contemporaries. It was so accurate that it could measure the distance from the earth to the moon to within one foot of accuracy.

--------------------------------------------------------------------------------------

DC low power PoE  charging sell phones etc is one thing, running more power than that is definitely not in the building code. The battery area of a garage or shed is about the only place for DC cables from the battery to the inverter/charger/solar controllers.

Small cabins on an island might be fine but a pretty small market. Good Luck